How did ancient Chinese determine
seasons? Ancient Chinese determined seasons and the passage of time
through the astronomical phenomena at early evening, mansions (also known as
lunar lodges, lunar mansions, constellations, xiu) in the southern sky and
the Big Dipper (the Plough).

.... Yao separately commanded Xizhong to reside at Yanggu .... The day is
of the medium length and the star (mansion, constellation) is Niao. You may
thus exactly determine mid-spring .... .... He further commanded Xishu
to reside at Nanjiao .... The day is at its longest, and the star is in Huo.
You may thus exactly determine mid-summer.... .... He separately
commanded Hezhong to reside at Meigu, .... The night is of the medium
length, and the star is Xu. You may thus exactly determine mid-autumn....
.... He further commanded Heshu to reside at Youdu, .... The day is at
its shortest, and the star is Mao. You may thus exactly determine
mid-winter....

(mid-winter, winter solstice, mansion Mao)

(mid-spring, spring equinox, mansion Niao)

(mid-summer, summer solstice, mansion Huo)

(mid-autumn, autumnal equinox, mansion Xu)

The above pictures show the simulated phenomena in the southern sky at
early evening around 1700 BC.

Ancient Chinese also determined seasons and the passage of time through
the pointing direction of the handle of the Big Dipper (the Plough). In the
winter the "handle" points north at early evening, in the spring the
"handle" points east at early evening, and so on. The following animated
picture shows the astronomical phenomena in northern sky at early evening of
24 Jieqi around 450 BC. For the detail of twenty-four Jieqi, please refer to
the page Chinese
Calendar.

12 Houses of the Yellow Path (the path along which
the sun seems to move, or ecliptic)

It was great convenience to use lunar months for civil purposes in
ancient times because moon phases were obvious. Each year has approximately
twelve lunar months, which is the real reason why the Yellow Path
(ecliptic in Western astronomy) are
divided into twelve sections.

Ancient Chinese determined seasons through the pointing direction of the
handle of the Big Dipper (the Plough). In the winter the "handle" points
downward, north, at early evening. In the spring the "handle" points east at
early evening, and so on. Accordingly, ancient Chinese divided the horizon
into twelve sections and gave them names for linking the directions to which
the "handle" of Big Dipper points in twelve months. Twelve names of these
sections are Zi (north), Chou, Yin, Mao (east), Chen, Si, Wu (south), Wei,
Shen, You (west), Xu and Hai, and are known as twelve Terrestrial/Earthly
Branches. Each branch has its meaning, e.g.. Zi means to nurture. Finally,
the twelve Terrestrial/Earthly Branches were applied to the 12 houses of the
Yellow Path and arranged in clockwise direction.

Why was the direction of Chinese zodiac in reverse to western zodiac? It
is because what ancient Chinese drew were what they saw.

Ancient Chinese determined the passage of time through the astronomical
phenomena, mansions, in the southern sky at early evening. Stars move from
east to west every night. The order of mansions, zodiacal constellations, on
the Chinese zodiac just only describes the order of appearances of mansions
according to actual phenomena in southern sky.

Ancient Chinese astronomers divided the sky into three Enclosures,
twenty-eight Mansions and four Images/Symbols/Quadrantal Xiu. Seven Mansions
form one Image. The Four
Images are the Azure
Dragon, the Vermilion Bird, the White Tiger and the Murky Tortoise.

According to historical books, at least one Armillary Sphere at the
Ancient Observatory is graduated in ancient Chinese unit of angles (degree,
Du, ), 365.25 degrees to the circumference, to match the year length.
It was convenience to set a circumference of 365.25 degrees for astronomical
calculation and prediction, because ancient astronomers used to believe that
the sun moved among the stars (mansions) and returned to the same star
(mansion) after 365.25 days, and the sun moved along the equator at constant
speed.

Water clock, clepsydra with 100 markings (also known as Ke/Tu/
Du/degrees), were the earliest timekeeper for measuring the passage of time,
the lengths of day and night, midnight especially. This device divided a day
into 100 parts.

It seems probable that before Han dynasty ancient Chinese only determined
the coordinates of the sun on the year's shortest day and longest day.
Ancient Chinese determined the equatorial coordinate of the sun through the
observation of the star (mansion) in the southern sky at the midnight when
the gnomon showed the year's longest day. At the midnight the sun was right
on the opposite side to the star (mansion) which crossed the meridian.

12 Ci means twelve sections on the celestial equator. The Sun,
Moon and the planets apparently move through them in seasonal order. These
sections are Xingji, Xuanxiao, Zouzi, Jianglou, Daliang, Shichen, Chunshou,
Chunhuo, Chunwei, Shouxing, Dahuo and Ximu. The following table was compiled
according to the chapter CI DU ( The Order and The Measurements) of
HAN SHU (History of the Han Dynasty). For the detail of Jie and Zhong
mentioned in the following table, please refer to the page Chinese
Calendar.